Abstract
For the nanopore sensing of various large molecules, such as probe-labelled DNA and antigen-antibody complexes, the nanopore size has to be customized for each target molecule. The recently developed nanopore fabrication method utilizing dielectric breakdown of a membrane is simple and quite inexpensive, but it is somewhat unsuitable for the stable fabrication of a single large nanopore due to the risk of generating multiple nanopores. To overcome this bottleneck, we propose a new technique called “two-step breakdown” (TSB). In the first step of TSB, a local conductive thin portion (not a nanopore) is formed in the membrane by dielectric breakdown. In the second step, the created thin portion is penetrated by voltage pulses whose polarity is opposite to the polarity of the voltage used in the first step. By applying TSB to a 20-nm-thick SiN membrane, a single nanopore with a diameter of 21–26 nm could be fabricated with a high yield of 83%.
Highlights
Nanopore sensing has become a powerful method for directly probing biomolecules in aqueous solution
Even smaller nanopores down to sub-2 nm in diameter can be fabricated by focused-electron-beam etching[23,24] or helium ion etching[25,26,27] by transmission electron microscopy (TEM) or helium ion microscopy (HIM)
Nanopore fabrication by dielectric breakdown has a great advantage in terms of fabrication cost; expensive equipment, such as that needed for electron beam (EB) lithography, TEM or HIM, is not required
Summary
Nanopore sensing has become a powerful method for directly probing biomolecules in aqueous solution. Morin et al prepared solid-state nanopores with diameters of approximately 20–30 nm to detect PNA-PEG-labelled DNA20 For such applications, the nanopore thickness does not need to be ultrathin, as is required for DNA sequencing with single-nucleotide resolution. Nanopore fabrication by dielectric breakdown has a great advantage in terms of fabrication cost; expensive equipment, such as that needed for EB lithography, TEM or HIM, is not required This method is rather unsuitable for the stable fabrication of a single large nanopore due to the risk of generating multiple nanopores[33,34,36,37] when trying to widen a nanopore by additional voltage stresses. The stable fabrication of a single large nanopore (larger than 20 nm in diameter) in a thick SiN membrane (20 nm in thickness) via dielectric breakdown is demonstrated. It was practically impossible to fabricate a single nanopore, regardless of its size
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